Senior Security Engineer, Research & Engineering (United Kingdom)

Location: Remote within the United Kingdom

Who We Are:

Founded in 2012 by 3 expert hackers with no investment capital, Trail of Bits is the premier place for security experts to boldly advance security and address technology's newest and most challenging risks. It has helped secure some of the world's most targeted organizations and devices. Our combination of novel research with practical solutions reduces the security risks that our clients face from emerging technologies. Our work helps drive the security industry and the public's understanding of the technology that underlies our world.

Cybersecurity preparedness is a moving target. Companies like ours are the tip of the spear in the fight against attackers. Our research-based and custom-engineering approach ensures that our clients' capabilities are at the forefront of what's available. For companies and technologies that live and die by their security, a proactive, tailored approach is required to keep one step ahead of attackers.

Democratizing security information is essential. As part of our business, we provide ongoing informational support through blogs, whitepapers, newsletters, meetups, and open-source tools. The more the community understands security, the more they'll understand why a company like ours is so unique and valuable.

Role

AI has transformed the cost curve for formal verification. Network boundaries, infrastructure, operating system components, cryptographic libraries, and proof-checking kernels can now ship with genuine mathematical guarantees attached, and those guarantees are narrower than the word "verified" leads anyone to believe. We are looking for candidates who have both the rigor to read a proof and say exactly what it establishes, and the instinct to find what it left out.

Day-to-day, you will evaluate specifications alongside their designs and proofs, and determine what has actually been established versus what has merely been assumed. Then, using state-of-the-art tools and frontier AI models, you will go after everything the proof does not reach. Some of what you find may be ordinary memory corruption. More of it will be a threat model that ignores a real attacker, a trusted computing base that does not survive deployment, or a sound proof of a property adjacent to the one that matters.

Red-team evaluations are scheduled for a one-week sprint with seven weeks to prepare. The tooling you build during that time determines how much ground you cover once the window opens. Trail of Bits is AI-native, and we expect AI to drive the bulk of our evaluations with agentic harnesses, triage pipelines, automated exploit generation, and systems like Buttercup , our cyber reasoning system that placed second at DARPA's AI Cyber Challenge.

You will work in small teams and with third parties and report to a domain lead in applied cryptography and proof systems, operating system internals, applications, hardware, or AI infrastructure. Several engagements will run simultaneously and remain separate, so holding information where it belongs matters as much as the technical work. Occasionally, you will attend sprints and hackathon events in London.

What You'll Achieve

• Break systems built to resist you. Compromise designs and production software whose authors had a proof assistant on their side, and demonstrate it with a working exploit rather than a written argument.
• Map the real attack surface of a proof. Establish the formal property, the level it holds, the threat model behind it, and the underlying assumptions, then show the client which of those give way under pressure.
• Build the tooling that decides your coverage. Design and extend the AI-driven discovery and triage systems that determine how much of a target a single engineer can reach within a short window.
• Write the assessment that becomes the record. Set out what held, what did not, and what you attempted without success, clearly enough that the result stands up to the product developers.
• Raise the practice around you. Publish tooling and methodology, write for the blog, present internally, and pull what one engagement learns into the next.

What You'll Bring

• Red teaming. Direct experience with red teaming production software, personally responsible for finding and proving exploitable vulnerabilities. Hands-on offensive work, not exercise coordination or scanner triage.
• Building AI tools that find bugs. Experience building AI-driven tooling for vulnerability discovery, such as agentic harnesses, LLM-assisted triage pipelines, or automated exploit generation. You have written this tooling, not only used someone else's.
• Formal methods. Experience applying formal methods to system designs and code implementations, including reading specifications and proof artifacts and reasoning about what a machine-checked proof does and does not establish. You can read at least one of Lean, Rocq, F*, Dafny, or Verus/Rust.
• Depth in a systems domain. Experience finding vulnerabilities in network protocol implementations, operating system internals, open-source software, cryptographic implementations, or AI inference infrastructure.
• Software development. Experience in Python, C++, and/or Rust.
• Written findings for expert readers. Experience producing security assessment reports for an audience that will scrutinize every claim.
• Delivery to a fixed external schedule with defined acceptance criteria.
• Vulnerability Disclosure. Experience in the ethical reporting of vulnerabilities in technology.

Preferred Qualifications

• Published vulnerability research: CVEs, advisories, or talks at venues like OffensiveCon, RECon, CCC, or USENIX Security.
• Experience auditing or contributing to a formally verified codebase such as HACL*, EverCrypt, seL4, CompCert, or CakeML.
• Experience building automated bug-finding infrastructure at scale: cyber reasoning systems, fuzzing fleets, or symbolic execution engines.
• Experience with zero-knowledge proof systems, proof-checking